This research deals with findings in perifusion experiments, in each of which a stream of incubation fluid of composition predetermined and varied as described by the experimenter is moved at predetermined rate(s) around anterior pituitary explants, or explants excised from the hypothalamus, and effluent samples are collected over predetermined time intervals for use in estimations of hormone release rates - of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) by pituitary explants, and of luteinizing hormone releasing hormone (LH-RH) by hypothalamic tissue explants. This approach is in use for, or planned for use in studies on: (a) how rapidly LH-RH, theophylline, 60 mM K ion and 10 minus to the 5th power M. Cu2 ion act, in comparison with one another in inducing LH and FSH releases from perifused anterior pituitary explants; (b) how rapidly, if at all, certain agents including acetylcholine, dopamine, 60 mM K ion and electrical stimulation act to induce LH-RH release from perifused hypothalamic tissue explants; (c) how long an agent effective at inducing LH release, or FSH release, of LH-RH release, continues to be effective if used at originally effective dosage for a prolonged period; agents of interest are listed in (a) and (b) above; (d) how perifusion experiments may best be done to provide data amenable to statistical analysis; procurement of such data in experiments on possible alteration in sensitivity of pituitary tissues to LH-RH, and of hypothalamic tissues to an agent effective at inducing LH-RH release, which may occur during the estrus cycle, or as result of estradiol administration.